UK 1, an unusual bis-benzoxazole metabolite isolated from Streptomyces sp. 517-02, is an inhibitor of topoisomerase II (Topo II) and hepatitis C viral replication. It is an antifungal and an antibiotic, and displays a wide spectrum of potent anticancer activities against lymphoma, leukemia, and certain solid tumor-derived cell lines with IC50 values as low as 20 nM. However, UK 1 is devoid of antimicrobial activity and is inactive against Pseudomonas aeruginosa and Staphylococcus aureus, a methicillin-resistant strain of S. aureus. Additionally, UK-1 can bind a wide variety of di- and tri-valent metal ions, particularly Mg2+ ions, and form complexes with DNA in the presence of Mg2+ ions. Topo II are ATP-dependent enzymes, which can simultaneously cut both strands of the DNA helix to manage DNA supercoils and tangles.

In vitro: UK 1 strongly blocked the growth of human epitheloid carcinoma HeLa, mouse melanoma B16, mouse leukemia P388 cells with ED50 values of 1.22 μg/ml, 1.17 μg/ml, and 0.11 μg/ml, respectively. UK 1 did not display any growth inhibitory activity against bacteria, fungi and yeasts up to 100 μg/ml [1].

In vivo: Up to now, in vivo study of UK 1 is still in the development stage.

Reference:
[1].  UEKI, M., UENO, K., MIYADOH, S., ABE, K., SHIBATA, K., TANIGUCHI, M., & OI, S. UK-1, a novel cytotoxic metabolite from Streptomyces sp. 517-02. I. Taxonomy, fermentation, isolation, physico-chemical and biological properties. The Journal of Antibiotics. 1993; 46(7): 1089-1094.